The resin monomer HEMA inhibits LPS-stimulated cytokine release

Objectives: Lipopolysaccharide (LPS) released from cariogenic Gram-negative microorganisms and compounds of non- polymerized dental adhesives or composites are available in deep cavities and might simultaneously influence vital functions of dental pulp cells. Therefore, we analyzed the effect of the resin monomer HEMA (2-hydroxyethyl methacrylate) on the LPS-stimulated release of pro- and anti-inflammatory cytokines from immunocompetent cells.
Methods: RAW264.7 mouse macrophages were exposed to HEMA (0-1-4-8mM) in the presence of 0.1 µg/ml LPS for 24h, and the expression of the redox-sensitive transcription factor Nrf2 in macrophages was activated by 25µM tBHQ (tert-butylhydrochinone). The release of the pro-inflammatory cytokines TNFα and IL-6 as well as the anti-inflammatory IL-10 was detected in cell culture supernatants using ELISA (enzyme-linked immunosorbent assay). Amounts of released cytokines were summarized as medians and differences between medians (plus 25% und 75% percentiles) were analyzed using the Mann-Whitney-U Test (α = 0,05).
Results: No increase of cytokine release from mouse macrophages was observed in the presence of HEMA alone. LPS-stimulated release of cytokines TNFα, IL-6 or IL-10 was inhibited by increasing HEMA concentrations. A 1000-fold increase in the release of TNFα induced by LPS was reduced by 1, 4 or 8 mM HEMA about 5-10-fold. TBHQ-induced expression of the cytoprotective Nrf2 counteracted the inhibitory effect of HEMA on the release of TNFα. An effect of Nrf2 on the HEMA-inhibited release of IL-6 or IL-10 was not detected.
Conclusions: HEMA inhibits LPS-stimulated cytokine release as an essential function of immunocompetent cells. This effect is probably caused by HEMA-induced oxidative stress as suggested by the protective influence of Nrf2 as a regulator of cell redox homeostasis.